1. Field of the Invention
The present invention relates to liquid crystal display devices, and more particularly, to a method of manufacturing a liquid crystal display (LCD) panel.
2. Background of the Related Art
With the rapid development of information communication, the importance of displays that image information is high. One device, the Cathode Ray Tube (CRT) can display a wide range of colors with excellent brightness. However, the need for high resolution, large screen portable display devices has lead to the development of flat panel displays. Flat panel displays are widely used for imaging in computers, spacecraft, and aircraft.
Flat panel displays include liquid crystal display (LCD), electroluminescent displays (ELD), field emission displays (FED), and a plasma display panels (PDP). An ideal flat panel display would be lightweight, have high luminance, high efficiency, and high resolution, would operate with a fast response time, using low voltage and with low power consumption, all at low cost, while producing natural colors. While not completely ideal, the active matrix color LCD panel has become widely used.
Generally, an active matrix color LCD panel is formed by attaching an active matrix substrate (“TFT” substrate) to a color filter substrate. While generally successful, misalignments between the two substrates can reduce manufacturing yield. One suggestion for preventing misalignment is to form color filters by electrodeposition. Electrodeposition uses potentials between gate and data pads to produce the color filters on the TFT substrate.
A related art method of manufacturing an LCD panel will now be described. FIG. 1 and FIGS. 2A–2E show plan views of a related art LCD panel. The related art LCD panel includes a TFT substrate and a color filter substrate. The TFT substrate has an active region and a pad region. The pad region includes a gate pad region Gpad and a data pad region Dpad.
A gate line 11 and a crossing data line 15 are arranged on the TFT substrate (see, for example, FIG. 2B). A TFT is located near the crossing. A pixel electrode 17 (see FIG. 2C) connects to the TFT. Additionally, R, G, B color filters are formed on the pixel electrode 17 by electrodeposition (see, FIG. 2E).
Referring now to FIG. 2A, a gate pad 11b is formed in the gate pad region. The gate pad 11b electrically connects to a gate driving circuit (not shown) and transmits driving signals to a gate line 11. Referring now to FIG. 2B, a data pad 15c is formed in the data pad region. The data pad 15c electrically connects to a data driving circuit (not shown) and transmits image signals to a data line 15.
For reference, although not shown, more than one gate pad and one data pad are formed. During manufacture the various pads are electrically shorted together by shorting bars to prevent damage to the thin film transistors that are formed as shown in FIG. 2C. The shorting bars are subsequently removed.
Referring now to FIG. 2D, a black matrix 19 is arranged on the color filter substrate to prevent light from leaking around the gate line 11 and the data line 15.
A method of manufacturing the aforementioned LCD panel will be described with specific reference to FIGS. 2A to 2E. As shown in FIG. 2A, a metal layer is formed, such as by sputtering, on an insulating substrate. That metal layer is then patterned to form a gate line 11 and a gate electrode 11a in an active region, and a gate pad 11b. As shown, the gate pad 11b extends to form a single conductive path with the gate line 11.
Afterwards, a gate insulating film (not shown) is formed over the exposed surfaces, including over the gate pad 11b, beneficially by chemical vapor deposition (CVD). A semiconductor layer 13 is then formed over the gate electrode 11a. The semiconductor layer 13 forms a TFT channel.
Referring now to FIG. 2B, subsequently, a metal layer is formed on the gate insulating film, such as by sputtering, and then patterned to form a data line 15 that crosses the gate line 11. Source and drain electrodes 15a and 15b on the semiconductor layer 13 are also formed, as is a data pad 15c in the data pad region Dpad. The data pad 15c extends to form a single body with the data line 15.
Then, a passivation film (not shown) is formed over the active region and the pad region. Then, as shown in FIG. 2C, a contact hole is formed to expose the drain electrode 15b and opening are formed to expose the gate pad 11b and the data pad 15c. A transparent conductive material is then formed over the exposed surfaces. The transparent conductive material is subsequently patterned to form a pixel electrode 17 that electrically connects with the drain electrode 15b through the contact hole. Additionally, transparent conductive films 17a that electrically connect with the gate pad 11b and the data pad 15c are also formed. Those films assist connecting the gate pad and the data pad to external driving circuits. Indium tin oxide (ITO) is usually used as the transparent conductive material.
As shown in FIG. 2D, a black matrix layer 19 is then formed. The black matrix layer 19 prevents light from leaking around the gate line 11, the data line 15 and the TFT. At this time, the transparent conductive films 17a that connect to the gate pad 11b and to the data pad 15c remain exposed.
Referring not to FIG. 2E, the TFT substrate is dipped in an aqueous solution. A voltage is then applied through the pixel electrode 17 where a first color filter will be formed. A first color filter layer 21a is then electrodeposited on a corresponding pixel electrode. A second color filter layer 21b and a third color filter layer (not shown) are formed in a similar manner.
Although not shown, a sealant is located at predetermined positions on the TFT substrate. The TFT substrate is then attached to an opposing substrate (not shown). By injecting and sealing a liquid crystal therebetween, the related art process for manufacturing the LCD panel is completed.
Unfortunately, the foregoing related art method of manufacturing an LCD panel has problems. When color filters are formed by electrodeposition, the color filter material is deposited from an aqueous solution. Since such aqueous solutions are typically corrosive, the exposed transparent conductive films of the pad regions are eroded. In other words, in the related art, when color filters are electrodeposited the transparent conductive films on the gate pad and on the data pad are exposed. The exposed transparent conductive films are eroded by the aqueous solution used for electrodeposition. Such erosion increases the ohmic contact resistance and reduces that device reliability.
To prevent the transparent conductive films from being eroded those films could be masked before electrodeposition. However, masking requires a separate mask and additional processing steps, thereby increasing the manufacturing cost and complexity. Therefore, a new method of manufacturing an LCD panel in which transparent conductive films are protected from erosion would be beneficial. Even more beneficial would be such a method that does not require a separate mask or additional processing steps.